Preparation of cyanoesters

ABSTRACT

A process for the preparation of certain cyano substituted esters and optical isomers thereof useful as insecticides by dehydration of the precursor carboxamido esters.

This invention relates to a process for the preparation of certain cyanosubstituted esters useful as insecticides, and to certain novel isomericforms of such esters produced thereby.

Elliott et al (Nature (1974), 248, 710) has reported the isolation ofthe insecticide (S)-α-cyano-3-phenoxybenzyl(IR,cis)-3-(2,2-dibromovinyl)-2,2-dimethylcyclopropane carboxylate, bycrystallisation from the mixture of the two diastereoisomers which wereobtained by esterifying (IR,cis)-3-(2,2-dibromovinyl)-2,2-dimethylcyclopropane carboxylic acid withracemic α-cyano-3-phenoxybenzyl alcohol. The corresponding mixture ofdichlorovinyl compounds has been prepared (Elliot et al, Pesticide Sci(1975), 6, 537) but the constituent corresponding to the abovedibromovinyl compound has not been isolated. It may be inferred thatthis dichlorovinyl derivative will also be a very potent insecticide. Itis desirable therefore to prepare the isolated individual dichlorovinyldiastereoisomers viz (S)-α-cyano and (R)-α-cyano-3-phenoxybenzyl(IR),cis)-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane carboxylates forevaluation as insecticides.

A preliminary examination of the mixture of diastereoisomers, an oil,indicated that separation by physical methods might be difficult.Obviously the most direct method for the production of the two isomerswould be to esterify the cyclopropane carboxylic acid with the twoenantiomers of α-cyano-3-phenoxybenzyl alcohol. Of the latter the (R)form has been prepared by Elliott et al (Nature (1974), 248, 710) byasymmetric addition of hydrogen cyanide to 3-phenoxybenzaldehyde in thepresence of the enzyme D-oxynitrilase. Resolution of a cyanhydrin by theusual resolution techniques, for example via a diastereoisomericprecursor, has not been achieved. It is likely that the conditionsnecessary for the liberation of the cyanhydrin from a diastereoisomericprecursor will also racemise the cyanhydrin. Optically activebenzaldehyde cyanhydrin, for example, is known to racemise underextremely mild conditions.

However methods involving enzyme treatment even if effective on thesmall scale are not really suitable for manufacture. We have thereforedevised an alternative technique, utilising novel carboxamidoesterswhich does not rely upon enzyme treatments.

According to the present invention a process for the preparation of acompound of formula: ##STR1## wherein R represents either (a) a group offormula: where X is chlorine, bromine or methyl, or (b) a group offormula: ##STR2## where Y is chlorine or methyl and n is one or two, andR² is an alkyl group containing from 2 to 4 carbon atoms; and R¹ is aphenoxy or 2,2-dichlorovinyloxy group; comprises the step of treating acompound of formula: ##STR3## with a dehydrating agent.

A useful dehydrating agent is a phosphorus oxyhalide, for example,phosphorus oxychloride, and the process step is conveniently carried outby bringing a solution of the oxyhalide in a suitable solvent, forexample a chlorinated hydrocarbon solvent such as methylene dichloride,into contact for a period of from about 30 minutes to about 30 hourswith a solution of the compound of Formula II in a suitable solvent suchas for example pyridine, at a temperature within the range -20° to +50°C., preferably within the range -10° to about +20° C.

It will be appreciated by those skilled in the art that in the compoundsof Formula I the carbon atom to which the cyano atom is attached issubstituted by four different groups or atoms and the compounds willshow optical isomerism, as will the compounds of Formula II. Theinvention process may be used to convert racemates of Formula II to theracemate of Formula I, or it may equally well be used to convertcompounds of Formula II in the (R)- or (S)-configuration to thecorresponding isomers of the compounds of Formula I whilst retaining thestereochemical configuration around the optically active centre. That isthe conversion from carboxamido to cyano occurs without racemisation orinversion or loss of optical purity. Thus the process is extremelyuseful in preparing individual stereochemical isomers of the compoundsof Formula I.

Thus for example (S)-α-cyano-3-phenoxybenzyl(1R,3R)-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane carboxylate maybe prepared from (S)-α-carboxamido-3-phenoxybenzyl(1R,3R)-3-(2,2-dichlorovinyl)-2,2-dimethyl-cyclopropane carboxylate.

Other compounds which may be prepared by the invention process includethe following:

(S)-α-cyano-3-phenoxybenzyl(1R,3R)-3-(2,2-dibromovinyl)-2,2-dimethylcyclopropane carboxylate,

(S)-α-cyano-3-(2,2-dichlorovinyloxy)benzyl(1R,3R)-3-(3,3-dichlorovinyl)-2,2-dimethylcyclopropane carboxylate,

(S)-α-cyano-3-phenoxybenzyl (1R,3R)-chrysanthemate,

(S)-α-cyano-3-phenoxybenzyl (+)-2-(4-chlorophenyl)isovalerate, and

(S)-α-cyano-3-(2,2-dichlorovinyloxy)benzyl(+)-2-(4-chloro-phenyl)isovalerate,

together with the corresponding (R)-α-cyano compounds.

The preparation of the compounds of Formula II is fully set out in ourcopending U.K. patent application No. 24931/76 entitled"Carboxamidoesters", and is also set out herein.

Particular compounds which are typical examples of compounds of FormulaII include the following:

(+)-α-carboxamido-3-phenoxybenzyl(+)cis-trans-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane carboxylate,

(S)-α-carboxamido-3-phenoxybenzyl(1R,3R)-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane carboxylate,(S)-α-carboxamido-3-(2,2-dichlorovinyloxy)benzyl(1R,3R)-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane carboxylate,

(+)-α-carboxamido-3-phenoxybenzyl (+)-(4-chlorophenyl)isovalerate,

(S)-α-carboxamido-3-phenoxybenzyl (+)-(4-chlorophenyl)isovalerate,

(S)-α-carboxamido-3-phenoxybenzyl(1R,3R)-3-(2,2-dibromovinyl)-2,2-dimethylcyclopropane carboxylate.

The compounds of Formula II may be prepared by reacting a compound offormula: ##STR4## where Q is halogen, preferably chlorine, with analcohol of formula: ##STR5## optionally in the presence of a base.

Conveniently the above process may be performed by dissolving thealcohol of Formula IV in a suitable solvent in the presence of a base,or the solvent itself may be the base (e.g. pyridine) and adding to thesolution a solution of the acid halide of Formula III in a suitablesolvent, for example a hydrocarbon solvent, such as benzene or toluene,at a temperature within the range -5° to +30° C., preferably the ambienttemperature. Although the reaction may be accelerated or completed bythe application of heat, it is often sufficient merely to allow thereaction to proceed at the ambient temperature. The product may beisolated and purified by conventional techniques.

Alternative processes for the preparation of the esters of the inventioninclude for example reaction of the acid of formula: ##STR6##(optionally in the form of its salt) with a halide of formula: ##STR7##or reaction of the acid of Formula V with the alcohol of Formula IV inthe presence of a suitable acid catalyst.

Optically active compounds of Formula II may be prepared by reactingtogether optically active compounds of Formulae III or V with opticallyactive compounds of Formulae IV or VI as appropriate, or by reaction ofone optically active compound with a racemate of the other reactantfollowed by separation of the diastereoisomeric isomers by differentialsolubility e.g. by fractional crystallisation.

Thus, reaction of the (S)-isomer of an alcohol of Formula IV with theracemic form of a compound of Formula III (e.g. the (+)-cis-form of acompound of Formula III where R is a group of Formula A) to give a pairof diastereoisomers, which for convenience could be termed (+) (S) and(-) (S), and these could be separated by the use of fractionalcrystallisation techniques.

The alcohols of Formula IV are themselves novel compounds.

Compounds of formula: ##STR8## wherein R is hydroxy, amino or alkoxycontaining from 1 to 4 carbon atoms, and ammonium salts of suchcompounds wherein R is hydroxy, are particularly useful as intermediatesin the preparation of the carboxamidoesters of Formula II.

Examples of specific compounds useful as intermediates include:

racemic 3-phenoxymandelic acid,

(S)-3-phenoxymandelic acid,

(R)-3-phenoxymandelic acid,

racemic 3-phenoxymandelamide,

(S)-3-phenoxymandelamide,

(R)-3-phenoxymandelamide,

racemic methyl 3-phenoxymandelate,

methyl (S)-3-phenoxymandelate,

methyl (R)-3-phenoxymandelate,

and examples of ammonium salts include the l-(-)-α-methylbenzylammoniumand the d-(+)-α-methylbenzylammonium salts of racemic, (R)- and(S)-3-phenoxymandelic acids.

The compound of formula VII wherein R is OH may be obtained by thehydrolysis of 3-phenoxybenzaldehyde cyanhydrin, and it may be resolvedinto its constituent (R) and (S)-isomers by conversion to the salt of anoptically active amine, for example α-methylbenzylamine. The salts maythen be separated by their differential solubility characteristic e.g.by fractional crystallisation.

The hydrolysis of the cyanhydrin is preferably carried out using acidconditions, for example by heating the cyanhydrin with a dilute mineralacid in aqueous alcoholic solution for a period of from about 30 minutesto several hours. The process may be carried out using for exampleaqueous ethanolic hydrochloric acid at a temperature within the range65° to 90° C., and may be supplemented by a period of treating thereactants with aqueous caustic alkali solution at a similar temperature.When the hydrolysis is complete the acid obtained may be purified bymaking a suitable water soluble salt, for example the sodium salt, toseparate the acid from water insoluble material, and reprecipitating atpH less than 7 by using a mineral acid.

The compounds of formula VII wherein R is alkoxy as defined may beobtained for example by treating the 3-phenoxymandelic acid with anappropriate alcohol in the presence of an acid catalyst. This processmay be conducted at the ambient temperature using for example an excessof the alcohol containing dissolved hydrogen chloride. Alternativelyother methods of esterification may be used such as treating the alcoholwith 3-phenoxy-mandelic acid halide in the presence of a base.

The compounds of formula VII wherein R is amino may conveniently beprepared by treating the alkyl esters of 3-phenoxymandelic acid withammonia under pressure, for example by adding the ester to liquidammonia at low temperature, and allowing the mixture to warm up to theambient temperature in a sealed vessel.

The above processes may be used in sequence to convert3-phenoxybenzaldehyde cyanhydrin to 3-phenoxy-mandelamide, and thislatter compound either as the racemate or as the (R)- or (S)-isomer canbe used for example in the preparation ofα-carboxamido-3-phenoxybenzyl-3-(2,2-dihalovinyl)-3,3-dimethylcyclopropanecarboxylates, which are themselves precursors for the insecticidallyactive α-cyano-3-phenoxybenzyl3-(2,2-dihalovinyl)-3,3-dimethylcyclopropane carboxylates.

In a further aspect the invention relates to isolated fully resolvedisomeric forms of an ester of3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane carboxylic acid.

The substance α-cyano-3-phenoxybenzyl3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane carboxylate possessesthree asymmetrically substituted carbon atoms in its structure and cantherefore theoretically exist in eight different isomeric forms. None ofthese forms has yet been described in isolation, although certainmixtures have been described in U.K. Patent specification No. 1,413,491.

The invention process involving dehydration of the precursor carboxamidoesters allows each of these isomeric forms to be prepared in asubstantially optically pure state.

Accordingly this invention provides in isolation in a substantiallyoptically pure state each of the isomers of the compoundα-cyano-3-phenoxybenzyl 3-(2,2-dichloro-vinyl)-2,2-dimethylcyclopropanecarboxylate, that is -

(S)-α-cyano-3-phenoxybenzyl(1R,3S)-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane carboxylate(Compound IX),

(r)-α-cyano-3-phenoxybenzyl(1R,3S)-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane carboxylate,

(S)-α-cyano-3-phenoxybenzyl(1S,3R)-3-(2,2-dichlorovinyl)-2,2-methylcyclopropane carboxylate,

(R)-α-cyano-3-phenoxybenzyl(1S,3R)-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane carboxylate,

(S)-α-cyano-3-phenoxybenzyl(1R,3R)-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane carboxylate,

(R)-α-cyano-3-phenoxybenzyl(1R,3R)-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane carboxylate,

(S)-α-cyano-3-phenoxybenzyl(1S,3S)-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane carboxylate,

(R)-α-cyano-3-phenoxybenzyl(1S,3S)-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane carboxylate.

As set out hereinabove the method of preparing the compounds involvesthe dehydration of the corresponding α-carboxamido derivatives ofFormula II. Thus, for example, Compound I can be prepared from the exactstereochemically equivalent α-carboxamido compound, that is,(S)-α-carboxamido-3-phenoxybenzyl(1R,3R)-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane carboxylate.

The value of this process lies in the fact that (a) there is no changeor loss of optical activity through inversion or racemisation and, (b)the diastereoisomeric forms of the α-carboxamido intermediates aresolids and are easily separated by their differential solubilitycharacteristics (in contrast to the known mixtures of the α-cyanoisomers which are liquids) by for example frictional crystallisationtechniques.

The individual isolated isomers of the invention have insecticidalproperties, but each isomer has its own spectrum of activity and someisomers are intrinsically more active than others, and more active thanthe non-resolved material. Thus Compound IX is several times more activethan the known (+)-α-cyano-3-phenoxybenzyl(+)-(50:50/cis-trans)-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropanecarboxylate. It is interesting that the activity of the isomers inisolation is not necessarily in direct proportional relationship totheir activity when present in the non-resolved material. This raisesthe possibility of actually mixing two or more of the isolated isomerstogether in various proportions to obtain a material with a particularinsecticidal action, and could lead to the development of highlyspecific insecticidal preparations which would not affect non-targetorganisms adversely.

As stated above the individual isomers of Formula I are useful asinsecticides, and are most conveniently used as such when formulatedinto compositions. In another aspect therefore the invention providesinsecticidal compositions which comprise as an active ingredient anisomer of the compound α-cyano-3-phenoxybenzyl3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane carboxylate, in asubstantially optically pure state, in association with agriculturallyand horticulturally acceptable diluent or carrier materials.

In a preferment of this aspect of the invention the active ingredient is(S)-α-cyano-3-phenoxybenzyl(1R,3R)-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane carboxylate.

The compositions are for use in agriculture or horticulture but the typeof composition used in any instance will depend upon the particularpurpose for which it is to be used.

The compositions may be in the form of granules or powders comprisingthe active ingredient and a solid diluent or carrier. The compositionsmay also be in the form of liquid preparations to be used as dips orsprays which are generally aqueous dispersions or emulsions.

The compositions to be used as sprays may also be in the form ofaerosols wherein the formulation is held in a container under pressurein the presence of a propellant such as fluorotrichloromethane ordichlorodifluoromethane.

For agricultural or horticultural purposes, an aqueous preparationcontaining between 0.0001% and 1.0% by weight of the active ingredientor ingredients may be used.

The compositions of the present invention may, if desired, also comprisein addition to an isomer of the present invention, at least one otherbiologically active ingredient, for example, an insecticide or afungicide. They may also comprise a synergist of the type useful insynergising the activity of pyrethroids type insecticides.

In use, the invention compounds or compositions may be used to combatinsects in a variety of ways. Thus the insects themselves, or the locusof the insects or the habitat of the insects is treated with a compoundor a composition according to the invention.

The invention also provides a method of treating plants to render themless susceptible to damage by insects, which comprises treating theplants, or the seeds, corms, bulbs, tubers, rhizomes or otherpropagative parts of the plants, or the medium in which the plants aregrowing with an isomer or insecticidal composition according to theinvention.

Thus the compounds of the invention are toxic towards a wide variety ofinsect and other invertebrate pests, including for example thefollowing:

    ______________________________________                                        Tetranychus telarius                                                                             Blattella germanica                                        Aphis fabae        Musca domestica                                            Megoura viceae     Pieris brassicae                                           Aedes aegypti      Plutella maculipennis                                      ______________________________________                                    

The invention is illustrated by the following Examples, in whichExamples 1 to 8 illustrate the preparation of intermediates and Example9 illustrates the dehydration of the intermediate carboxamidoester tothe corresponding nitrile.

EXAMPLE 1

This Example illustrates the preparation of racemic 3-phenoxymandelicacid.

A mixture of 3-phenoxybenzaldehyde cyanhydrin (208 g), ethanol (600 ml)and concentrated hydrochloric acid (400 ml) was kept at the ambienttemperature for 24 hours, after which it was concentrated by evaporationunder reduced pressure. 2N Sodium hydroxide solution (500 ml) was addedto the residue and the mixture heated at 80° C. for one hour, cooled,concentrated hydrochloric acid (250 ml) added to it, and the resultantmixture heated at 80° C. for a further hour. The volatile portion wasremoved by evaporation under reduced pressure and the residue stirredwith a solution of sodium bicarbonate (60 g) in water (60 g). Theaqueous solution was decanted from the undissolved oil, stirred withactivated charcoal, filtered, and the filtrate acidified withhydrochloric acid. The precipitated solid was collected by filtrationand dried to yield racemic 3-phenoxymandelic acid, m.p. 131° C.

EXAMPLE 2

This Example illustrates the resolution of racemic 3-phenoxymandelicacid.

l-(-)-α-Methylbenzylamine (21.0 g) was added to a solution of racemic3-phenoxymandelic acid (67.0 g) in isopropyl alcohol (700 ml) and themixture kept for 24 hours at the ambient temperature. The solidprecipitate was collected by filtration, (the filtrate kept -- seebelow) and recrystallized twice from isopropyl alcohol (200 ml) to yieldthe l-(-)-α-methylbenzylammonium salt of (S)-3-phenoxymandelic acid,m.p. 153° C. This was then shaken with a mixture of diethyl ether (150ml) and 5N hydrochloric acid (25 ml), the ether layer separated, washedwith water, dried over anhydrous magnesium sulphate and concentrated byevaporation of the ether under reduced pressure to yield a residue ofsolid (S)-3-phenoxymandelic acid, m.p. 110°-112° C., [α]_(D) ²⁵ + 85°(C, 1.5, methanol).

The isopropyl alcohol solution obtained as a filtrate in the aboveprocess was concentrated by evaporation under reduced pressure untilreduced to a volume of 50 ml. This was then shaken with 2N hydrochloricacid (150 ml) and the resultant solid precipitate collected byfiltration. This solid (impure (R)-3-phenoxymandelic acid) was dissolvedin isopropyl alcohol (400 ml) and d-(+)-α-methylbenzylamine (17.0 g)added to the solution. After keeping the mixture at the ambienttemperature for a period of 24 hours the solid precipitate was collectedby filtration, and recrystallised twice from isopropyl alcohol (200 ml)to yield the d-(+)-α-methylbenzyl-ammonium salt of (R)-3-phenoxymandelicacid, m.p. 154° C. Free (R)-3-phenoxymandelic acid was obtained fromthis salt by treatment in the manner described above for the isolationof the (S)-isomer. The (R)-isomer had m.p. 112° C., [α]_(D) ²⁵ -84° (C,1.0, methanol).

EXAMPLE 3

This Example illustrates the preparation of (S)-3-phenoxymandelamide.

(S)-3-Phenoxymandelic acid (13.0 g) was added to a solution of dryhydrogen chloride (15.0 g) in methanol (100 ml) and the solution thusobtained kept at the ambient temperature for 24 hours after which periodthe volatile portion was evaporated yielding methyl(S)-3-phenoxymandelate as a residual oil. This was then added to liquidammonia (20 ml) in a pressure vessel which was then sealed andtemperature of the mixture allowed to rise to the ambient temperatureover a period of 24 hours. The vessel was then opened and the excess ofammonia allowed to evaporate. The residual material was stirred withwater and the solid collected by filtration, and recrystallised frombenzene (70 ml) to yield impure (S)-3-phenoxymandelamide, m.p. 93° C.[α]_(D) ²⁵ + 25.4° (C, 2.0, methanol), (approximately 80% opticallypure).

Optically pure material was obtained using the following procedure:

A suspension of the impure (S)-3-phenoxymandelamide (7.5 g) in a mixtureof benzene (150 ml) and n-butanol (6 ml) was stirred at 25° C. for 30minutes. The undissolved solid was separated by filtration and thefiltrate was evaporated. The residue was recrystallised from benzene togive optically pure (S)-3-phenoxymandelamide, m.p. 94° C., [α]_(D) ²⁵ +30° (c, 2.0, methanol).

Further optically pure (S)-3-phenoxymandelate was obtained by repeatingthe above purification procedure using the undissolved solid separatedfrom the benzene/n-butanol mixture.

EXAMPLE 4

By using a procedure similar to that illustrated in the previousExample, (R)-3-phenoxymandelamide, m.p. 94° C., [α]_(D) ²⁵ -30° (c. 2,methanol) was obtained starting from (R)-3-phenoxymandelic acid, via themethyl ester and after final purification of the initially isolated 80%optically pure (R)-3-phenoxy-mendelamide, m.p. 93° C., [α]_(D) ²⁵ -25.3°(c. 2.0, methanol).

EXAMPLE 5

By using a procedure similar to that illustrated in the two previousExamples, racemic 3-phenoxymandelamide, m.p. 109° C., was obtained viaracemic methyl 3-phenoxy-mandelate (m.p. 71° C.).

EXAMPLE 6

This Example illustrates the preparation of(S)-α-carboxamido-3-phenoxybenzyl(1R,3R)-3-(2,2-dichloro-vinyl)-2,2-dimethylcyclopropane carboxylate.

A solution of (1R,3R)-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropanecarboxylic acid chloride (0.45 g) in benzene (2.0 ml) is added at 5° C.to a solution of (S)-3-phenoxymandelamide (0.5 g) in pyridine (1.0 ml),and the mixture is kept at the ambient temperature for 24 hours. Afterthis period the mixture is acidified with dilute hydrochloric acid, thebenzene layer separated, washed with water and with aqueous sodiumbicarbonate solution, dried and concentrated by evaporation of thebenzene under reduced pressure. The residual oil is treated withcyclohexane (10 ml), and the precipitated solid collected by filtrationand dried to yield (S)-α-carboxamido-3-phenoxybenzyl(1R,3R)-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane carboxylate, m.p.131° C.

EXAMPLE 7

This Example also illustrates the preparation of(S)-α-carboxamido-3-phenoxybenzyl(1R,3R)-3-(2,2-dichloro-vinyl)-2,2-dimethylcyclopropane carboxylate.

A solution of (1R,3R)-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropanecarboxylic acid chloride (0.44 g) in benzene (2.0 ml) was added to asolution of racemic 3-phenoxymandelamide (0.5 g) in pyridine (1.0 ml) at5° C. The mixture was kept for 24 hours at the ambient temperature andthen acidified with dilute hydrochloric acid. The benzene layer wasseparated and washed with aqueous sodium bicarbonate solution. Afterconcentration of the benzene solution by evaporation under reducedpressure to a volume of 1.0 ml, cyclohexane (3.0 ml) was added and themixture kept at the ambient temperature. A solid (m.p. 124°) wasprecipitated on keeping, and this was collected by filtration andrecrystallised from a mixture of benzene and cyclohexane to yield(S)-α-carboxamido-3-phenoxybenzyl(1R,3R)-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane carboxylate, m.p.131° C., identical with the product obtained in the previous Example.

The benzene/cyclohexane mother liquors contained impure(R)-α-carboxamido-3-phenoxybenzyl(1R,3R)-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane carboxylate.

EXAMPLE 8

The procedure of the previous Example was used to prepare(S)-α-carboxamido-3-phenoxybenzyl(1R,3R)-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane carboxylate, m.p.131° C., identical with the product obtained in the previous Example,from racemic cis-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropanecarboxylic acid chloride (0.65 g) and (S)-3-phenoxymandelamide (0.5 g).The benzene/cyclohexane mother liquors contained impure(S)-α-carboxamido 3-phenoxybenzyl(1S,3R)-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane carboxylate.

EXAMPLE 9

This Example illustrates the preparation of (S)-α-cyano-3-phenoxybenzyl(1R,3R)-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane carboxylate.

A solution of phosphorus oxychloride (0.33 g) in methylene dichloride(1.0 ml) was added dropwise over a period of 5 minutes to a solution of(S)-α-carboxamido-3-phenoxybenzyl(1R,3R)-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane carboxylate (0.5g) in pyridine (1.5 ml) whilst the temperature was maintained at -5° C.The mixture was then stirred at 0° C. for one hour, after which it wasdiluted with benzene and poured into dilute hydrochloric acid. Thebenzene layer was separated, washed with water and with aqueous sodiumbicarbonate solution, dried and concentrated by evaporation of thebenzene to yield a residue of (S)-α-cyano-3-phenoxybenzyl(1R,3R)-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane carboxylate, m.p.54° C., which on recrystallization from petroleum ether gave the purematerial m.p. 57° C.

EXAMPLE 10

This Example illustrates the improved insecticidal properties of theisomer (S)-α-cyano-3-phenoxybenzyl(1R,3R)-3-)2,2-dichlorovinyl)-2,2-dimethylcyclopropane carboxylate(Compound IX) in comparison with the unresolved(+)-α-cyano-3-phenoxybenzyl(+)cis-trans-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane carboxylate(containing about 40% cis and 60% trans material -- Compound X).

Mustard plants are grown in pots until they reach the 7 to 8 leaf stageand then sprayed with aqueous compositions of the chemicals under testusing a hand held spray gun operated at 15 psig. The plants are sprayedto maximum retention (just prior to run off) the spray being directed toboth the upper and lower surfaces of the leaves. The aqueouscompositions are prepared by dissolving the active ingredient in a smallamount of acetone and mixing the solution with water to which 0.1% of anemulsifying agent (`Lissapol NX`) has been added. (`Lissapol` is a TradeMark).

When dry the plants are transferred to a constant environment chamber inwhich the temperature is maintained at 25° C. and relative humidity at50%. Day length is controlled at 16 hours by the use of mercury vapourlamps. For each treatment a leaf is removed from the plant and placed onfilter paper in a loosely covered petri dish (9 cm diameter) andinfested with five half grown larvae of either Plutella xylostella orPhaedon cochleariae. Leaves are so removed and infested at intervals ofzero, one, two, three and seven days, and assessed for mortality of thelarval after 72 hours. Three replicates are used in each test.

The following Tables indicate the results obtained.

    __________________________________________________________________________                      % MORTALITY                                                         RATE      DAYS AFTER TREATMENT                                                                          PEST                                        COMPOUND                                                                              PARTS/MILLION                                                                           0   1  2  3  7  SPECIES                                     __________________________________________________________________________    IX      3.9       100 93 80 20 53 Plutella                                            1.9       53  73 40 13 13 xylostella                                  X       3.9       67  80 33 0  0                                                      1.9       33  27 25 27 7                                              IX      3.9       93  93 80 87 53 Phaedon                                             1.9       80  33 60 7  53 cochleariae                                 X       3.9       27  27 40 7  53                                                     1.9       13  0  0  7  13                                             __________________________________________________________________________

The results clearly show that at equivalent rates the isolated isomer IXis considerably more active as an insecticides than the double racematemixture of cis and trans isomers, represented by Compound X.

I claim:
 1. A process for the preparation of a compound of formula:##STR9## wherein R represents either (a) a group of formula: ##STR10##where X is chlorine, bromine or methyl, or (b) a group of formula:##STR11## where Y is chlorine or methyl and n is one or two, and R² isan alkyl group containing from 2 to 4 carbon atoms; and R¹ is a phenoxyor 2,2-dichlorovinyloxy group; comprises the step of treating a compoundof formula: ##STR12## with a dehydrating agent at a temperature fromabout -10° to about +20° C.
 2. A process as claimed in claim 1 in whichthe dehydrating agent is a phosphorus oxyhalide.
 3. A process as claimedin claim 2 in which the phosphorus oxyhalide is phosphorus oxychloride.4. A process as claimed in claim 1 carried out in the presence of aliquid diluent material.
 5. A process as claimed in claim 4 in which theliquid diluent material includes pyridine.
 6. A process as claimed inclaim 4 in which the liquid diluent material includes a chlorinatedhydrocarbon solvent.